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| Dissertation / PhD Thesis/Book | PreJuSER-40409 |
2004
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/274
Report No.: Juel-4144
Abstract: This thesis deals with quantitative studies of equilibrium and non-equilibrium phenomena on Pt(III) and Cu(100) surfaces using scanning tunneling microscopy (STM). The aim of this work is apply theoretical methods based on statistical physics to determine atomistic energy parameters of surface diffusion processes on metal substrates which cannot be directly detected, and hence, analyzed as individual atomic hopping events. As was shown previously, one may determine activation barriers of diffusion, pre-exponential factors and formation energies. In this thesis, the theoretical methods were applied to Pt(111) and Cu(100) substrates and step free energies were measured, dominant mass transport processes were identified and the relevant activation energies were obtained. On Pt(III), for instance, the equilibrium shape and the equilibrium edge fluctuations of monatomic high islands were studied between 533 K and 713 K. Using the measured equilibrium shapes, the ratio between the step free energies of A- and B-steps on Pt(111) was analyzed for the first time as a function of temperature. Using the relatively new method of island edge fluctuation studies, absolute values for the free energies for A- and B-steps on Pt(111) could be determined experimentally for the first time. As a non-equilibrium phenomena, the Ostwald ripening of single-layer deep vacancy islands on Cu(100) was investigated between 323 K and 398 K. A previous result could be confirmed that the mono-vacancies are the dominant mass transport species on Cu(100). From the temperature dependence of the decay rate, the relevant activation energy have been obtained. Comparing the activation energy found in this thesis with previous measurements allowed the determination of the sticking barrier of mono-vacancies at vacancy island edges on Cu(100). A further island decay process was studied in this work which has been discovered only recently to accelerate island decay on fcc(111) surfaces, the rapid island decay. In this thesis, it is shown that this fast decay channel exists also on Pt(111). Finally, a coarsening process is discussed which has a great importance on fcc (100) surfaces, the island coalescence. Here, the coalescence of single-layer deep vacancy islands on Cu(100) was investigated between 303 K and 353 K. It could be shown that the equilibration of the island shape after coalescence is dominated by atom diffusion along the island edges. The relevant activation energy was determined and the result corroborates recent preliminary studies of fluctuations of highly-kinked steps which showed that the activation energy is much lower compared to the energy measured for steps along the atomically dense direction.
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